The invention relates to extreme pressure lubricating oils, particularly alkali metal borate-containing lubricants.
Alkali metal borate-containing lubricants are well known in the art for their usefulness as extreme pressure lubricating oils. See, for example, U.S. Pat. Nos. 3,313,727, 3,565,802, 3,819,521, 3,846,313, 3,853,772, 3,907,691, 3,912,639, 3,912,643, 3,912,644, 3,997,454, and 4,089,790.
The borate-containing oils, described in these patents, have a serious deficiency in service. If water is introduced into the system containing the borate lubricant, the borate crystallizes out of the oil and forms hard granules. This crystallization decreases the extreme pressure function of the lubricant. Furthermore, it has been found that water contamination of the borate lubricant can lead to seal leakage. It is believed that the crystallization is caused by water contamination which leads to the formation of deposits on shafts at or near the seals. The turning motion of the shafts then slowly abrades the seals, thereby allowing loss of the lubricant.
U.S. Pat. No. 3,997,454 claims a hydrated potassium borate with a boron-to-potassium ratio of 2.5 to 3.5 as being superior to other alkali metal borates in resisting the adverse effects of water contamination.
U.S. Pat. No. 3,819,521 claims a lubricant composition containing a hydrated sodium borate and a C.sub.3 -C.sub.6 polyol containing two to six hydroxyl groups. This patent teaches the use of borate at concentrations of 2 to 25 parts by weight for each 75 to 100 parts oil which is essentially 2 to 25% by weight borate. The concentration of the C.sub.3 -C.sub.6 polyol is 0.3 to 1.0 parts per part of borate which is essentially 0.6 to 20 percent by weight of C.sub.3 -C.sub.6 polyol.
It is one object of the present invention to provide an alkali metal borate-containing lubricant having improved resistance to the adverse effects of water contamination.